frequently asked questions

What is the purpose of alt.video.dvd?
Discussion of DVD hardware and software for computers
and home entertainment systems; also information and
entertainment (movies) released on DVD.

Can I advertise in alt.video.dvd?
All advertising, whether "on-topic" or not, is subject
to being reported to the sender's ISP and/or web host.

Advertising is:
- Any offer to sell or trade.
- Any message designed to drive traffic to the
sender's web site.
- Any message designed to generate email responses.

A 4-line or less "sig" attached to a legitimate
question or comment is not considered advertising.

What is DVD?
DVD stands for Digital Versatile Disk. It is a
multi-purpose technology suited to both entertainment
and computer uses.

A DVD is identical in thickness (1.2 millimeters) and
diameter (120 millimeters or 4.7 inches) to a standard
Compact Disc, but that's where the similarities end.
The DVDs storage capacity is seven times that of a
CD, with a 4.7-gigabyte capacity on a
single-side/single-layer DVD. That's the data-storage
equivalent of a 133-minute movie, thus allowing 95
percent of all movies to fit comfortably on a
single-layer DVD, eliminating the need for "flipping"
the disc and leaving extra room for multiple audio,
language, and subtitle tracks; bonus materials; menu
screens; and other features unique to DVD. This
capacity is nearly doubled (8.5 GB) on a
single-side/dual-layer DVD, and quadrupled (17 GB) on
a double-side/dual-layer DVD, allowing DVD to flourish
not only as a movie-lover's format, but as an
amazingly flexible medium (DVD-ROM) for
high-definition computer games and multimedia
applications. In short, this makes DVD the home
entertainment and multimedia format of the new
millennium.

What are the features of DVD-Video?
The main features of the various DVD formats are:
- Backwards compatibility with current CD media.
- All DVD hardware will play audio CDs and CD-ROMs
- Physical dimensions identical to compact disc but
using two 0.6 mm thick substrates, bonded together.
- Single-layer/dual-layer and single/double sided
options.
- Up to 4.7 GB read-only capacity per layer, 8.5 GB
per side maximum.
- Designed from the outset for video, audio and
multimedia, not just audio.
- All formats use a common file system (UDF).
- Digital and analog copy protection for DVD-Video
and DVD-Audio built into standard.
- Recordable and re-writable versions.

Not only do movies look great on DVD, but they also
include lots of interesting additional material and
interactive options. The DVD format was designed from
the beginning to support interactive features
including menus and indexing, alternate audio and
video tracks, and even user-controlled branching
within the material.

Most movies also include additional material such as
movie trailers and behind-the-scene documentaries, and
sometimes additional scenes that were cut from the
movie. DVDs can provide support for the hard of
hearing and for alternate languages.

The alternate audio track also is often used for a
director's commentary, in which the entire movie is
accompanied by voice-over discussion by the creative
team, describing their thinking while it was being
created and edited.

Some DVDs also provide multiple camera angles for the
video, so you can switch points of view as it plays.

Why is the quality of DVD-Video so much better
than VHS?
DVD video is a higher resolution than VHS. Standard
VHS video has 320 dots per line and DVD video has
720 dots per line. However, DVD video quality still
depends on many production factors (including the amount
of compression used) and the display device it is viewed on.

DVDs will usually (but not always, see dvd rot) last much
longer than videotape.

Will DVD replace VCRs?
Eventually. DVD has many advantages over VCRs,
including fundamentally lower technology cost for
hardware and disc production.

What is MPEG?
DVD video is compressed from studio CCIR-601 format to
MPEG-2 format. This is a "lossy" compression which
attempts to remove redundant information (such as
sections of the picture that don't change) and
information that's not readily perceptible by the
human eye. The resulting video, especially when it is
complex or changing quickly, may sometimes contain
"artifacts" such as blockiness or fuzziness. It
depends entirely on the quality of compression and
how heavily the video is compressed. At average rates
of 3.5 Mb/s (megabits/second), artifacts may be
occasionally noticeable. Higher data rates result in
higher quality, with almost no perceptible difference
from the original master at rates above
6 Mb/s. As MPEG compression technology improves,
better quality will be achieved at lower rates.

MPEG-4 is the current state-of-the-art for video
compression technology. The two older technologies
MPEG-1 and MPEG-2 already caused a widespread
distribution of digital video on the PC and notebook.
The successor of MPEG-4 is already on the horizon and
is called MPEG-7. This video standard principally
integrates an object search routine. MPEG-2 will also
be extended; MPEG-21 is the succeeding standard.

What are "regional codes," "country codes," or "zone
locks"?
Motion picture studios demanded that the DVD standard
include codes which can be used to prevent playback of
certain discs in certain geographical regions. Players
sold in each region will have that region's code built
into the player. The player will refuse to play discs
which are not allowed in the region. This means that
discs bought in one country may not play on players
bought in another country.

Regional codes are entirely optional. Discs without
codes will play on any player in any country. It's not
an encryption system, it's just one byte of
information on the disc that the player checks. Some
studios have already announced that only their new
releases will have regional codes. Presumably, once a
DVD movie has achieved worldwide release it could be
re-released without encoding.

I tried to copy a DVD. Why didn't it work?
Copying DVDs is prohibited by the DMCA (Digital
Millennium Copyright Act) and usually prevented with a
Macrovision (or equivalent) circuit in every DVD
player. Composite video output will have a rapidly
modulated colorburst signal along with pulses in the
vertical blanking signal to confuse the
automatic-recording-level circuitry of VCRs.
Unfortunately, this can degrade the picture,
especially with old or nonstandard equipment.

Macrovision is designed to guard against casual
copying (which the studios claim causes billions of
dollars in lost revenue), but it doesn't stop pirates.

What is the DMCA?
The DMCA is the Digital Millennium Copyright Act,
passed by the U.S. Congress in 1998, supposedly to
update copyright law for electronic commerce and
electronic content providers. Unfortunately, this law
is very poorly written, and is now regularly used by
corporations to restrain the three primary concessions
of copyright and otherwise prevent free speech
activity:

1. Fair use is the right to make unauthorized copies
of works for certain protected purposes - mainly for
academics, reporting, or criticism. When a student
quotes a book in a high school paper, she is making a
fair use, and can't be stopped by the copyright owner.

2. First sale is the right to sell purchased media
over and over again, as long as you don't make any
copies. When you read a book, then sell it to a used
book store to be bought and read by someone else,
you're exercising your rights under first sale.

3. Limited time - copyrights are granted for a limited
time. After that time expires, the work goes into the
public domain - it can be copied and used by anyone,
for any reason.

The DMCA has one particularly bad section, called the
anti-circumvention provision. That section makes it a
crime to break encryption used to prevent someone from
getting access to electronic content, or to "traffic"
in a tool used to do so.

A friend told me that if you cover the inner ring of a
DVD with a black marker, you will disable the
Macrovision. Is this true?
No, you can't disable Macrovision that way.

There is an audio-CD copy protection that can be
disabled that way - the disc contains phony data to
throw off CD-ROM players so they can't read the CD.
Audio-CD players will in theory not try to read that
data and ignore it but some are affected anyway. The
fake data is indeed located on the inner ring and can
be made unreadable by using a marker.

Is there a noticeable difference in the Superbit
version of a movie...?
The whole "point" of Superbit is to have superior
sound and video quality for the movie. If you compare
a superbit version with a non-superbit version,
chances are, superbit is better quality, even if there
are no extras... but now the studio seems to be
getting into "Superbit Deluxe" where one disc is a
high-quality video/audio transfer of the film, and the
second disc is a bunch of extras.

It takes good equipment to appreciate the difference.
Like a really good player (Pioneer Elite, Philips,
Marantz, Onkyo, etc.), good cabling, and an HDTV.

HDTV's, particularly 16x9 HDTV's, can not only show
the full resolution that a DVD sends, but can also
engage an anamorphic mode which delivers 2-3 times the
resolution normally allowed. With this kind of
resolution available, the improved quality of Superbit
can be seen.

What happens if I scratch the disc?
DVD includes a better error-correction system than CD.
Most scratches will cause minor raw data errors that
are easily corrected. Major scratches may cause
anything from unrecoverable errors that will show up
as a momentary glitch in the picture to a complete
failure.

Is CD-ROM compatible with DVD-ROM?
Yes. All DVD-ROM drives will read CD-ROMs (Yellow
Book). However, DVD-ROMs are not readable by CD-ROM
drives.

Will DVD support Digital TV (HDTV)?
HDTV is not supported by DVD, but the designers have
it in mind. Since HDTV uses MPEG-2 it will be easy to
"upgrade" the DVD format. The limited data rate of DVD
may make it difficult to support high-quality HDTV,
but this can be solved by either increasing the spin
rate (as with multi-speed CD-ROM drives) or
using higher-capacity blue lasers.

Some have speculated that a "double-headed" player
reading both sides of the disc at the same time could
double the data rate. This is impossible since the
track spirals go in opposite directions. The DVD specs
would have to be changed to allow reverse spirals on
the second side.

What are the sizes and capacities of DVD?
There are many variations on the DVD theme. There are
two physical sizes: 12 cm (4.7 inches) and 8 cm (3.1
inches), both 1.2 mm thick. This is the same form
factor as CD. A disc can be single-sided or
double-sided. Each side can have one or two layers of
data. The amount of video a disc can hold depends on
how much audio accompanies it and how heavily the
video and audio are compressed. The oft-quoted figure
of 133 minutes is apocryphal: a standard DVD can
actually hold up to 6 hours of video and audio if it's
heavily compressed (which reduces the quality).

What are aspect ratios?
Video can be stored on a DVD in 4:3 format (standard
TV shape) or 16:9 (widescreen). The 16:9 format is
"anamorphic," meaning the picture is squeezed
horizontally to fit a 4:3 rectangle then unsqueezed
during playback. DVD players output widescreen video
in three different ways:

Note: Some 16:9 discs are playable in widescreen and
letterbox modes only, if the producer chooses.

For letterbox mode the player uses a "letterbox
filter" that creates black bars at the top and the
bottom of the picture (60 lines each for NTSC, 72 for
PAL). This leaves 3/4 of the height remaining,
creating a shorter but wider rectangle. In order to
fit this shorter rectangle, the picture is squeezed
vertically by combining every 4 lines into 3. This
compensates for the original horizontal squeezing,
resulting in the movie being shown in its full width.

For pan & scan mode the video is unsqueezed to 16:9
and a portion of the image is shown at full height on
a 4:3 screen by following "center of interest"
coordinates that are encoded in the video stream
according to the preferences of the people who
transferred the film to video.

For anamorphic mode the video is stretched back out by
widescreen equipment to its original width.

In widescreen or letterbox mode if a movie is wider
than 16:9 (and most are), additional thin black bars
will be added to the top and bottom at production time
or the sides may be cropped (possibly with a small
amount of additional panning).

Video stored in 4:3 format is not changed by the
player. It will appear normally on a 4:3 screen.
Widescreen systems will either stretch it horizontally
or add black bars to the sides.

Some producers may put 16:9 source on one side of the
disc and 4:3 source on the other, since "full-frame"
4:3 movies have additional picture at the top and
bottom rather than panning and scanning. (The
cinematographer has two sets of frame marks in his
viewfinder, one for 4:3 and one for 1.85, so he can
allow for both formats).

The 16:9 anamorphic format causes no problems with
line doublers, since they simply double the lines on
their way to the widescreen display which then
stretches out the lines.

What is progressive scan?
One of the primary tasks of the MPEG decoder inside
every DVD player is to take the 24 fps data stored on
the DVD and convert it to 60-fields-per-second video
for TV viewing. Since 24 doesn't divide evenly into
60, a process called "3-2 pulldown" is employed, where
3 video fields are created from the first film frame,
then 2 fields from the next frame, then 3, then 2,
3-2-3-2-3-2, etc. The result is 60-fields-per-second
interlaced-scan video, and that's the end of the story
for non-progressive-scan DVD players.

Progressive-scan DVD players add an important
additional step to create a better-looking picture
they generate a progressive-scan video signal through
a process called de-interlacing (sometimes called
"line-doubling"). The de-interlacer's first task is to
look at the interlaced video signal as it leaves the
MPEG decoder and determine whether its original source
was 24-frame-per-second film or 30-frame-per-second
video. The original frame rate determines the type of
processing necessary to create an optimized
progressive-scan signal.

At least that's what progressive-scan DVD players
are supposed to do. However, most of the inexpensive
models just double up the lines and create even more
motion artifacts.

What is "DVD rot?"
DVD rot makes discs unplayable by impairing the
ability of their aluminum layer to reflect light. Its
most likely causes include oxidation caused by air
coming into contact with the reflective layer, a
galvanic reaction between a dual-layer disc's gold and
aluminum coatings, and a chemical reaction triggered
by impurities in either the disc's adhesive or in the
aluminum itself.

The vast majority of reported cases of DVD rot have
been shown to be due to poor quality control during
the manufacturing process or user mishandling. DVDs
are a delicate audio/video/data storage device that is
held together by a laminated outer surface containing
layers of plastic and reflective metal coatings, and
held together by special glues.

If manufactured with proper quality control at the
production line end, placed and removed properly from
its storage case when used, and stored properly by the
consumer, DVDs will definitely outlive their video
tape counterparts.

How can I convert some of my old home movies on VHS
and 8mm to DVD?
The "Guides" section of http://www.doom9.org/ has all
the information you need on this and many other DVD
topics.

I just got a DVD player and it pauses, skips and
pixilates a lot when I'm trying to watch a movie. What
causes that?
If you are having these problems on more than one disc
it's probably the DVD player. Inexpensive or
"throw-away" players are much less reliable than
higher-priced (>$100) models.

Which is the best video connection to use; RF,
composite, S-video or component?
Assuming you use decent quality cables, component
video is the best.
Ranked by quality from worst to best;
- RF
- Composite
- S-video
- Component

Where can I download movies off the net?
A reputable on-line retailer. You "upload" your CC
info, and then you can "download" all the movies you
want. Downloading commercial movies without paying is
illegal.

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